The present invention relates to a chuck having at least one jaw assembly that is radially displaceably guided in a chuck body and comprises a driving jaw and a clamping jaw, with the back side of the clamping jaw being adapted to be positively coupled with a coupling member that is mounted in the driving jaw in such a way as to be displaceable at right angles to guide means provided in the chuck body for the jaw assembly, with the coupling member being adapted to be uncoupled from the clamping jaw via eccentric means rotatably mounted in the driving jaw.
A chuck of this general type, in the form of a three-jaw chuck, is disclosed in DE-OS 34 37 505. With this known chuck construction, the axially fixed, yet rotatably mounted eccentric means engages in a transverse groove or slot that is provided on the upper side of the coupling member, so that rotation of the eccentric means results in an axial displacement of the coupling member. In a forward end position, teeth of the coupling member engage teeth formed on the back side of the clamping jaw, thereby positively holding the clamping jaw on the driving jaw in a form-locking manner. When the coupling member is displaced by the eccentric means into its rearward end position, the coupling member and the clamping jaw are uncoupled from one another, so that the clamping jaw is released from the driving jaw and can be removed from the chuck body in a radial direction.
With this known construction, in order to prevent an accidental turning of the eccentric means that would retract the coupling member out of its coupling position, a spring-loaded piston is provided in the coupling member that in the coupling position thereof engages in a transverse slot of the eccentric means. Unfortunately, this means for preventing rotation of the eccentric means depends upon the reliable effectiveness of the relatively small spring that loads the piston, and also requires that the path of the piston not be obstructed with dirt, chips, or other shavings.
It is therefore an object of the present invention to improve a chuck of the aforementioned general type in such a way that with a few sturdy components, a reliable, positive fixation of the coupling member in its coupling position is provided.